Provided is an operation apparatus which can suppress detachment of a retaining member for retaining a rotating operation knob from a circuit board, by a simple structure. Locked portions (67) which can be inserted into through-holes (22) formed in a circuit board (20) and which can bend in a specific direction parallel to the circuit board (20), are provided in a retaining member (60) for rotatably retaining a rotating operation knob (140). A locked protrusion (67b) projecting toward one side in the specific direction is provided on the rear end of each locked portion (67). The locked protrusion (67b) moves by a predetermined amount toward the other side in the specific direction when the locked portion (67) bends in the other specific direction, and accordingly, is allowed to pass through each through-hole (22). The locked protrusion (67b) is abutted against the underside surface of the circuit board (20) when the locked portion (67) is elastically returned after the locked protrusion passes through the through-hole (22). A deformation restriction portion (14) which is abutted against the locked protrusion (67b) from the other side so that the movement of the locked protrusion (67b) toward the other side is restricted so as to be less than a predetermined amount, is provided in a rear cover (10).